Enhance the configuration document

Author: hikalkan

docs/en/framework/architecture/modularity/basics.md

@@ -1,7 +1,5 @@
 # Modularity
 
-## Introduction
-
 ABP was designed to support to build fully modular applications and systems where every module may have entities, services, database integration, APIs, UI components and so on;
 
 * This document introduces the basics of the module system.

docs/en/framework/fundamentals/configuration.md

@@ -1,3 +1,52 @@
 # Configuration
 
-ASP.NET Core has an flexible and extensible key-value based configuration system. In fact, the configuration system is a part of Microsoft.Extensions libraries and it is independent from ASP.NET Core. That means it can be used in any type of application. See [Microsoft's documentation](https://docs.microsoft.com/en-us/aspnet/core/fundamentals/configuration/) to learn the configuration infrastructure. ABP is 100% compatible with the configuration system.
+ASP.NET Core has an flexible and extensible key-value based configuration system. The configuration system is a part of Microsoft.Extensions libraries and it is independent from ASP.NET Core. That means it can be used in any type of application.
+
+See [Microsoft's documentation](https://docs.microsoft.com/en-us/aspnet/core/fundamentals/configuration/) to learn the configuration infrastructure. ABP is 100% compatible with the configuration system.
+
+## Getting the Configuration
+
+You may need to get the `IConfiguration` service in various places in your codebase. The following section shows two common ways.
+
+### In Module Classes
+
+You typically need to get configuration while initializing your application. You can get the `IConfiguration` service using the `ServiceConfigurationContext.Configuration` property inside your [module class](../architecture/modularity/basics.md) as the following example:
+
+````csharp
+public class MyAppModule : AbpModule
+{
+    public override void ConfigureServices(ServiceConfigurationContext context)
+    {
+        var connectionString = context.Configuration["ConnectionStrings:Default"];
+    }
+}
+````
+
+`context.Configuration` is a shortcut property for the `context.Services.GetConfiguration()` method. You can use any of them (`IServiceCollection.GetConfiguration` is an extension method that can be used whenever you have an `IServiceCollection` object).
+
+### In Your Services
+
+You can directly [inject](dependency-injection.md) the `IConfiguration` service into your services:
+
+````csharp
+public class MyService : ITransientDependency
+{
+    private readonly IConfiguration _configuration;
+
+    public MyService(IConfiguration configuration)
+    {
+        _configuration = configuration;
+    }
+    
+    public string? GetConnectionString()
+    {
+        return _configuration["ConnectionStrings:Default"];
+    }
+}
+````
+
+## See Also
+
+* [Microsoft's Configuration Documentation](https://docs.microsoft.com/en-us/aspnet/core/fundamentals/configuration/)
+* [The Options Pattern](options.md)
+